Power to the people

The battery life of mobile phones is lagging behind other fast-changing advances in the technology. Andrew Lee and Helen Knight on the race to bring performance up to speed with 3G.

Arun Sarin, chief executive of Vodafone, did not mince his words when he addressed the great and the good of the mobile phone technology community at a recent industry conference.

The battery life offered by current handset models was ‘unacceptable’ and risked leaving the network operator’s customers disappointed, complained Sarin.

Vodafone and its competitors have spent billions of pounds building 3G phone networks and are champing at the bit to begin recouping that investment by offering their customers multimedia applications such as high-quality video and games.

That is difficult until the hardware – the handset and the battery that powers it – can deliver a level of performance that will not have frustrated consumers racing to cancel their subscriptions and leaving the mobile revolution dead in the water.

Mobile phones are the most high-profile example of a wider power deficit facing the consumer electronics industry, from laptop computers to games consoles and music players such as Apple’s iPod.

Manufacturers hope the emergence of a new generation of organic displays will reduce the power used by the screens of laptops, phones and other devices. Work is also underway to make antennas more efficient, leading to further power savings (see box below).

But the weakest link in the chain, as everyone agrees, is the battery.

‘Mobile handset battery power is approaching the upper limits of its physical capabilities,’ said Neil Mawston, senior analyst with technology research group Strategy Analytics. ‘Broadly speaking, battery power only doubles every eight to 10 years compared with one to two years for various internal components.’

According to Mawston, low battery power regularly comes high on the list of reasons why people want to change their mobile phone even given the present, relatively light, power demands of making voice calls and text messaging.

That ripple of dissatisfaction could easily turn into a torrent of disappointment, hence Sarin’s call for handset manufacturers to boost the power performance of their products. The phone makers in turn have passed the onus on to the power technology community.

Yrjo Neuvo, chief technology officer of Nokia, recently warned that mobiles will soon need 3W of power to support their demands with only 2W on the table from the available battery technology.

Those working in the field are well aware of the pressure from the consumer electronics industry. Dr. Gary Mepsted, technology manager for batteries, fuel cells and power systems at research giant Qinetiq, said battery R&D inevitably moves at a relatively slower pace than electronics.

‘Every step of the way batteries have to be qualified in terms of safety and transportability,’ said Mepsted. ‘But of course electronics developments move a lot faster, and I think that is where the problem has begun,’ he said.

However, progress is being made. Most mobile phones use lithium-ion and lithium-polymer batteries. These have much higher energy density than other materials such as nickel metal hydride and nickel cadmium, but are relatively expensive. Other materials now under development have much higher capacities, said Mepsted.’

Some of the technologies in the prototype stage are battery couples such as the lithium sulphur-polymer battery. The standard lithium-polymer battery in a mobile phone is around 100 watt-hours per kilogramme. Lithium sulphur at that size is around 1.5 times higher than that figure, and is also relatively low cost. The material is beginning to be commercialised, although it is not widely available at the moment,’ said Mepsted.

Researchers at Qinetiq are developing a battery using lithium-ion sulphide, which has double the energy of standard lithium-ion devices and is cheaper to produce as it uses iron rather than cobalt.

Lithium-ion sulphide is also safer to use than lithium-ion and lithium-polymer, as it does not undergo the same internal reaction when overcharged. This can cause batteries to produce heat and gas and explode. Some lithium-ion sulphide batteries are already commercially available, but not in a rechargeable form – a necessity for the mobile device market.

Qinetiq hopes to be producing rechargeable batteries based on the material in the next two to three years. Mepsted said the need for advanced power technology will leap as 3G networks come on stream over the next few years.

‘3G is extremely power-hungry, and talk-times and stand-by times have probably gone back to where they were in the 1980s. Some of these technologies have the potential to double the lifetime of the battery, and that has got to be equivalent to a more useable level,’ said Mepsted.

Even this magnitude of increase would not offer the levels that will be needed if phones are to become the mobile computers or games devices many sections of the industry are banking on. The only technology realistically capable of enabling this is the fuel cell. Fuel cell technology is beginning to emerge for mobile devices such as laptop computers thanks to work by industry giants such as NEC and Intel.

This is likely to lead to the development of hybrid power packs in which the fuel cell supports a conventional battery, allowing notebook computer manufacturers to reach their nirvana of eight hours of continuous operating capability within the next three years.However, major issues yet to be resolved – not least surrounding safety – mean it is likely to be some time before the batteries will be ready for use in smaller devices such as mobile phones.

Hydrogen fuel cells – the technology being investigated by car makers as an alternative vehicle power – are not suitable for mobiles, as the storage and generation of hydrogen on such a small scale is beyond the range of even the most ambitious researcher.

Instead, developers are putting their efforts into liquid fuel cells, and in particular direct methanol. Neat methanol, without taking into account the necessary fuel cell hardware, has a theoretical capacity of 6kWh/kg. There are significant technical hurdles to be overcome. Developers cannot use neat methanol, as it is highly toxic. Existing fuel cell membranes cannot prevent the gas permeating straight into the area around the user’s mouth. Until membranes impermeable to methanol can be produced diluted methanol must be used, reducing the capacity of the fuel cell.

‘On top of that it’s fairly low power because it’s a fairly slow reaction,’ said Mepsted.

It is also unclear how happy the world’s aviation industry would be to see its passengers boarding planes each carrying a little pack of highly volatile fuel. Few believe these problems are insoluble by Mepsted and his colleagues, however, and fuel cells are seen as the long-term answer to the mobile industry’s power deficit.

Strategy Analytic’s Mawston thinks they will be the ‘next big thing’ in mobile battery technology, with as many as six per cent of handsets worldwide equipped with the technology by 2010.

That still leaves the industry facing a power deficit. The likes of Vodafone don’t want – and cannot afford – to wait a decade for fuel cells to ride to the rescue of the multimedia mobile experience. In the meantime it is counting on advances in electronics to squeeze every last drop of efficiency out of the power that is available.

A key need is to minimise the power drain of the multimedia processing necessary to crunch the data required to deliver console-quality games and high-quality video to handset. This urgent requirement bodes well for technology companies that were quick off the mark in recognising power consumption as a looming issue for the industry.

One of these is Alphamosaic, a Cambridge processor specialist that emerged from research commissioned by mobile phone giant Orange in 1999, which led to the development of the world’s first videophone.

The device needed a 1980s-style ‘house-brick’ battery pack to support its massive data-processing requirements, prompting the Alphamosaic engineers to begin research into multimedia chip technology that could lower the power demands on mobile devices

Its microprocessor designs, which are already used in handsets built for the Asian market, allow console-style games to be played on mobile handsets while delivering a battery performance acceptable to consumers.

Dr. Robert Swann, co-founder of Alphamosaic, claimed that until recently power consumption was a factor mainly for designers of high-end manufacturers and early movers in the video-games-over-mobile market such as Korea’s Samsung.

‘It has not traditionally been at the top of the agenda. But we are now finding quite a lot of people in the middle to mass-market end of the industry viewing power consumption as a key issue,’ said Swann.With battery technology lagging so far behind consumers’ expectations companies such as Alphamosaic are likely to spend the next few years making hay while the sun shines.

Meeting the demands of the technology-hungry consumer

As if the electronics industry didn’t have enough to worry about simply preventing its devices from running out of power, consumers are upping the ante by demanding ever clearer, brighter display screens on which to view their picture messages and games.

Manufacturers are pinning many of their hopes in this area on organic light emitting diodes (OLEDs), a new generation of display materials that emerged from research carried out in the 1980s.

Though still a relatively young technology, OLEDs hold out the enticing prospect of thin, flexible high-quality display screens that require less power than the LCD, the dominant system used in most current devices.

OLEDs, and specifically light-emitting polymers (PLEDs), manipulate the tendency of certain organic materials to glow when subjected to an electrical current. Crucially in terms of power consumption, OLEDs generate their own luminescence. They do not require a backlight, removing one of the most power-hungry features of current mobile devices.

The UK’s Cambridge Display Technology (CDT), a spin-out from Cambridge University, is one of a group of global pioneers in the technology that also includes Kodak and Philips.

All three have announced significant technical and commercial progress during the past few months. Philips – which already has the 639 OLED ‘Magic Mirror’ phone on the market – said it had made two key breakthroughs towards higher-efficiency OLEDs, opening the way to high-volume, low-cost manufacturing.

The first is the development of a new anode layer that reduces energy wastage and boosts the luminosity of yellow and blue-emitting OLEDs. The second is a copolymer material capable of harnessing more efficient green and blue emissions.

Kodak unveiled its own OLED innovations just two weeks ago in the US. The company claimed its new material was the first to incorporate white pixels into an OLED panel, giving manufacturers the option of using white with a colour filter as well as red-green-blue displays.

CDT – which works with many of the big players in the OLED arena as a licensing partner – is also ramping up towards commercialisation through a development agreement with Sumitomo, one of Japan’s biggest chemical manufacturers and a long-standing research partner of the Cambridge company.

Another possible route to power saving, the antenna, is a particular challenge for the industry. The mobile phones of the next decade are likely to have to support several transmit/receive technologies simultaneously, adding to the power requirements of the handset.

Research is underway into new antenna systems. UK start-up company Antenova is building antennas using dielectric materials rather than metals. Dielectrics can be used to create systems that are smaller and more power efficient than is possible with metallic antennas, according to the company.